German Patent Document DE 33 43 076 A1 discusses a device which is provided for cooling an electric motor, which is provided as a drive motor in a motor vehicle, as well as for heating the passenger compartment of a motor vehicle. Fresh air or circulating air may be supplied to the passenger compartment of the motor vehicle as well as to the electric motor. For separating the two air circuits, a heat exchanger is provided which separates cooling of the electric motor from heating the passenger compartment of the motor vehicle. The electric motor may be cooled independently from the heating of the passenger compartment and the passenger compartment may be heated to the extent to which heat is output by the electric motor.
European Patent Document EP 596 000 B1 discusses a cooling circuit for a hybrid vehicle which contains an internal combustion engine, an electric motor, as well as a control circuit for the electric motor. After the start of the motor vehicle, the vehicle may be exclusively driven by the electric motor. The energy dissipation occurring in the control circuit and in the electric motor is used for heating the internal combustion engine for the purpose of shortening the cold-start phase of the internal combustion engine as much as possible. The cooling circuit contains a cooler which prevents an unacceptably high rise in the temperature in the cooling circuit. The cooling circuit contains a conventional coolant of the internal combustion engine as the heat carrier.
German Patent Document DE 199 51 735 A1 discusses a retarder system for supporting the brake of utility vehicles in which a retarder cooling circuit is provided for dissipating the heat generated in the retarder, the retarder cooling circuit containing transmission oil as the heat carrier. The transmission oil flow rate quantity may be increased or decreased independently from the transmission's operating conditions as a function of the mechanical load on the retarder for increasing the cooling performance and at the same time for lowering the temperature of the transmission oil.
A fluid-cooled internal combustion engine, which is situated in a motor vehicle for driving it, for example, is generally cooled by a coolant mixture of water and glycol, for example; the setpoint operating temperature of the internal combustion engine may be in a range of 90° C. to 110° C., for example.
Automatic transmissions in particular generally contain an oil pump in order to operate the actuators in the transmission via oil pressure and to ensure the lubrication of the transmission. A transmission oil cooling circuit may be provided due to the possible higher heat losses of automatic transmissions compared to normal manual transmissions. The operating temperature of a transmission is between 60° C. and 90° C., for example.